1. Field of the Invention
The invention relates to an apparatus for forging a hollow body from a preperforated hollow block, comprising forging tools that can be driven radially in relation to a forging axis, a clamping head which is displaceable on a guide bed in the direction of the forging axis and comprises collet chucks for the hollow block, and a mandrel carriage which is arranged on the side of the clamping head facing away from forging tools, which is displaceable independently of said clamping head along the guide bed, and whose mandrel bar provided with the forging mandrel penetrates the clamping head coaxially to the forging axis.
2. Description of the Related Art
For the purpose of forging long tubular hollow bodies from a pre-perforated hollow block it is known (EP 2 218 526 B1) to grip the hollow block in the region of a face end by the collet chucks of a clamping head comprising a through-hole which is coaxially to the collet chucks, so that the forging mandrel can be introduced by means of a mandrel bar through the through-hole of the clamping head into the hollow block for the subsequent forging of the hollow block between forging tools which can be actuated radially to the forging axis. This is ensured in such a way that the clamping head and the mandrel carriage accommodating the mandrel bar are independently displaceable from each other along a common guide bed. Since the forging mandrel is guided through the clamping head within the through-hole, the mandrel bar, which is offset in relation to the forging mandrel with respect to its diameter and is connected to a rotary drive in the mandrel carriage, requires a separate bearing element in order to enable centric guidance in the through-hole. This known forging apparatus is suitable for comparatively long tubular workpieces, but not for the forging of pre-perforated hollow blocks made of materials that are difficult to deform, because considerable forces occur between the clamping head and the mandrel carriage during the forging of such workpieces, which forces would need to be dissipated via the guide bed.
In order to reduce the overall length of forging apparatuses in which the perforated hollow block is clamped between a clamping head and a platen, it is further known (DE 195 23 280 C2) to mount the mandrel bar in the clamping head and to provide it with an axial actuating drive, so that the mandrel bar can be axially displaced for the purpose of forging hollow bodies in particular with an offset inside diameter in relation to the clamping head. Apart from the fact that the axial clamping of the preperforated hollow block between the clamping head and a platen requires additional construction work, there are also considerable limitations concerning the field of application of such forging apparatuses.
It is further known (DE 102010014583 A1) to provide carriages for the collet chucks and the mandrel bar which are displaceable on a common guide along the machine bed, of which the guide carriage for the collet chuck is driven by a spindle drive along the guide, whereas the mandrel carriage is connected to the guide carriage for the collet chuck by a further spindle drive. The mandrel carriage can thus be moved together with the guide carriage for the collet chuck along the machine bed, but can also be adjusted via the provided spindle drive in relation to the guide carriage for the collet chuck. Apart from the fact that the spindle drive between the guide carriage for the collet chuck and the mandrel carriage makes construction more complex and limits the adjusting possibilities for the mandrel carriage, the entire axial load of the mandrel carriage must be dissipated via the spindle drive for the mandrel carriage to the guide carriage for the collet chuck and from said carriage via its spindle drive to the machine bed.
The forging of a pre-perforated hollow block via a forging mandrel is used especially for economic reasons for tubular workpieces that need to be produced in comparatively small lots. This generally means that the forging apparatus needs to be a system with simple retooling features in order to enable the adjustment to different workpiece requirements. There is therefore a need in this connection to arrange an apparatus for forging hollow bodies in such a way that simple retooling can be ensured without having to accept any limitations in the field of applications such as the forging of comparatively long tubular hollow bodies or the forging of hollow bodies from a material that is difficult to deform.